I believe it was a vitamin thing and the owner sorted it out by putting supplements in their food.
Maybe do a search, or hopefully one of the people that helped out in the other thread will see this one

Niacin deficiency possibly? Infant's (the human kind) polyvisol who added extra iron can be given straight. You can buy plain niacin tablets and crush it up to add to their water. Or cou can get brewer's yeast and sprinkle it on their food.

Start on 150 mg niacin (from a capsule - do not use timed release or no-flush kind, just plain niacin) in each gallon of drinking water for 8 weeks. Results may be seen overnight, to within a week.

I am beginning to think about suggesting B complex because that includes thiamine, another B vitamin. Storey's Guide 1st Edition specifically recommends niacin (B3). But I have read here that thiamine deficiency also causes problems with ducklings.

Anyway, get the little on niacin, at least, right away.

If you cannot find it, use a tablespoon of brewer's yeast sprinkled on the food once daily.